This invention relates generally to plugs for telecommunications jacks and, more particularly, to an improved plug for DSX telecommunications jacks which permits monitoring of both transmit and receive circuit paths without injecting noise or breaking the electrical connections of these circuit paths. Throughout the telecommunicatioins industry, there are great numbers of test and monitor access jacks connected to networks. These jacks are used to provide access to circuits for testing, monitoring, and reconfiguring a telecommunications system by maintenance and service personnel.
There are currently several types of these jacks in use. However, the preponderance of installations consist of two main styles: the "310" jack and the "bantam" jack. These two styles differ only in the length and diameter of the jack and its associated mating plug. The electrical and mechanical properties of these two styles of jacks are otherwise the same. They have been in service in the telecommunications industry for many decades, resulting in hundreds of millions in service around the world today.
A typical jack module consists of three individual access jacks. The top jack is a monitor access point, which is used to monitor or listen to either the transmit or the receive side of a circuit, but not both, without disturbing the electrical signals present at the jack. The second jack, located just below the monitor jack, is usually wired as the transmit jack, to carry the data being transmitted to other equipment. Below the transmit jack is the receive jack, which carries the data coming from other equipment into the equipment in which the jack module is located. When the mating plug is inserted into either the transmit jack or the receive jack, the circuit path is broken, thereby interrupting the customer's traffic and introducing a service outage for the customer. On critical data circuits or circuits carrying many voice channels, this service interruption is unacceptable.
While inserting a mating plug into the monitor jack does not result in breaking the circuit path, the monitor jack can only be wired to a selected one of the transmit or receive circuit paths, thereby preventing monitoring of the other circuit path at this jack. In order to monitor the other circuit path, a second monitor jack must be provided at a different location at which the other circuit may be accessed.
In the past, the telephone company manually patched the transmission path using patch cables plugged into the transmit and receive paths of a circuit, while company personnel rewired the physical connections from the old equipment to the new equipment. When the rewiring was completed, the patch cables were pulled out of the jacks. However, each time the patch cables were plugged into or removed from one of the circuit paths, the customer's data was interrupted. This resulted in short dropouts, yellow alarms or even complete system failure for the customer, depending upon the skill of the company personnel performing the work. Because of the severe impact on customer data, telephone companies would typically schedule such work to be performed during maintenance windows between midnight and 2:00 A.M., and only following the time consuming step of obtaining a release from the customer. In addition, since telephone companies are regulated utilities, they are required to provide a minimum grade of service. Each time they perform work on a circuit that results in interruption of a customer's traffic, their overall grade of service is adversely affected. In summary, the manual patching of transmit and receive paths by telephone company personnel has generally been an unsatisfactory solution to the problem.
The need to access both transmit and receive circuit paths at a monitor access point has been more recently addressed by locating the far end of the circuit where the other circuit path originates. Sometimes, this is within the same central office, but oftentime is at a different central office or at the customer's location. More often than not, the other end of the circuit is located at some distance from the first end. This necessitates the use of mulitple pieces of test gear to monitor a single circuit since a single piece of equipment cannot physically reach the two remote ends of the circuit. Additional personnel, resulting in additional travel costs, are required at the far end of the circuit to monitor the other circuit path.
Typically, the transmit circuit path is wired to the monitor jack. In this way, each transmitter can be monitored, and the complete circuit can be analyzed. That is, transmit and receive paths for both ends of the circuit can be monitored since the transmit end of one circuit is connected to the receive end of the other and vice versa. This arrangement is known as a cross-connect, and the cross connections are made at the cross-connect shelves. The cross-connect shelves are used for circuit monitoring, testing, and rerouting.
The mating plug for this type of jack resembles a standard phono plug. It has a round circular tip that is electrically isolated from the ring portion of the plug, and both of these contacts are electrically isolated from the sleeve portion of the plug. The tip and ring contacts carry the actual data signals, while the sleeve is uaually left floating or is grounded. When the plug is inserted into the jack, the plug's tip and ring contacts make connection with the common side of the two internal contacts of the jack. When this occurs, the normally closed internal contacts are opened so that they no longer make connection to the common contacts within the jack, thus breaking the circuit. The plug and jack are designed so that the jack's contacts align with detents on the plug's tip and ring contacts, and the contact force applied by the jack hold the plug firmly in place. In the case of the monitor jack, the contacts are wired parallel with the circuit path that is to be monitored, so that inserting a plug into the monitor jack allows monitoring of the circuit without breaking or interrupting it. Internal 4000-ohm resistors are built into the jack's monitor port to prevent short circuiting the signals.
One known prior art solution to the problem discussed above has been to mill down a conventional circular mating plug of the type illustrated in FIG. 1A to be semi-circular in shape, as illustrated in FIG. 1B. When this modified plug is inserted into a jack with the flat milled surface facing the internal jack contacts, no contact is initially made with the internal jack contacts. In order to monitor the circuit to which the jack is connected, the modified plug is gently rotated until the tip and ring contacts thereof just touch the sides of the internal jack contacts. This solution is fraught with problems, not the least of which is unreliability. If the plug is not inserted into the jack correctly, the circuit will be broken. This undesirable result can occur even if the plug is only slightly misaligned. In addition, since the internal contacts of the transmit and receive jacks are rotated 180 degrees with respect to each other, it is very easy to insert the plug upside down, thereby breaking the circuit. As stated above, once the plug is inserted into the jack, it must be gently rotated to make connection with the internal jack contacts. However, if the plug is rotated too far, the circuit is again broken. Once rotated, the plug must be held in place since the retention mechanism in the jack that holds a conventional plug in place after insertion will not engage the modified plug. When the plug comes into contact with the internal jack contacts, it can cause them to move slightly horizontally, resulting in the introduction of noise into the circuit. Another problem with these modified plugs arises when the internal jack contacts are not in perfect vertical alignment. In this instance, the plug will only contact one of the two internal jack contacts. Rotating the plug more will cause that contact to open before the second contact is made.
In accordance with the present invention, plugs are provided for insertion into the conventional "310" or bantam styles of DSX telecommunications jacks to permit monitoring of both transmit and receive circuit paths without injecting noise into those circuit paths and without any risk of interrupting or breaking those circuit paths. Because these two styles of conventional jacks differ in size, two sizes of plugs are necessary. However, both sizes of plugs are identical in operation and function.